Trading a Cy Young winner is not unique. It now has happened 10 times in just the past 58 months — three times involving Cliff Lee and twice Zack Greinke. Heck, Travis d’Arnaud has been a key component in the return package twice.

You know what is unique? Getting a meaningful return for this kind of ace.

This is where theory differs from results. In theory, teams unlikely to contend in the near future should leverage a 38-year-old knuckleballer — no matter his hardware or popularity — into a high-end mix of prospects. The applause heard round the majors for the Mets doing just that with R.A. Dickey has been loud and sustained.

“No question about it,” an AL executive said, “this was a home run for the Mets. Sandy Alderson did an amazing job.”

But if you think you have heard such applause in the recent past, you have, in part because prospects never have been more treasured and hyped than now. Yet of the nine Cys moved between Johan Santana in February 2008 and Greinke last July, what resonates is generally how little impact the team acquiring the prospects has received.

Trumpets carried Matt LaPorta (for CC Sabathia), Kyle Drabek (for Roy Halladay) and Justin Smoak (when Lee was dealt to the Rangers) to their new teams, but the music mainly has petered out. Remember how the Mets almost walked away from the Santana talks because they didn’t want to give up Deolis Guerra, who the Twins outrighted off their 40-man roster this month.

The best such trade over the past four years was made two offseasons ago when the Royals dealt Greinke to the Brewers for what is now their starting shortstop (Alcides Escobar) and center fielder (Lorenzo Cain) plus a pitcher (Jake Odorizzi), who was just part of the package that helped Kansas City obtain James Shields and Wade Davis from Tampa Bay. Still, we hardly are talking high-end star power in exchange for an ace.

Which leads us back to the Mets and theory vs. results. Ultimately, Alderson’s regime will not be judged by their thought process. This is not a lab experiment. Regardless of how many victory laps any organization takes for being ranked high on, say, the Baseball America prospect list, there is no confetti, parade or historical significance to that.

Alderson behaved rationally and properly in turning Carlos Beltran into Zack Wheeler, and Dickey into d’Arnaud and Noah Syndergaard. But his Mets legacy, in many ways now, will be about whether this formed the cornerstone for sustained winning in the near future; whether the further patience he is asking Met fans to endure is rewarded by Wheeler and Syndergaard pitching to d’Arnaud during a bunch of NL East titles from 2015-20. It is about results.

There was consensus among executives with whom I spoke that the Mets did better in return than any of the other clubs who recently dealt former Cys. That is because Toronto executives truly believed the Mets would keep Dickey for either his $5 million next year or extend him themselves unless they received two high-end prospects. And here were the Blue Jays feeling they were an ace away from maximizing their go-for-it offseason. And, as unconventional as Dickey is, Toronto believes he is an ace.

Thus, after an initial rejection, Toronto buckled just before the Winter Meetings and included d’Arnaud, a must-have in the Mets’ reasoning to do this deal. Early last week the concession was to include Syndergaard and protect Aaron Sanchez, who the Jays believe is a less-polished pitching prospect than Syndergaard, but has a higher ceiling.

Syndergaard generally will be viewed as one of the majors’ 30-40 best prospects while d’Arnaud will be in the top 10, in part because it is so hard to find quality young catching. The projection is not for Buster Posey, but for high-end solid. The worry is about health. In the past three years, d’Arnaud has missed time due to a concussion and injuries to his back, thumb and knee. The Mets gave d’Arnaud a physical and feel there are no worries. Yet, at the most demanding position, d’Arnaud has found a way to get hurt a lot at a young age.

Syndergaard is 6-foot-5, throws hard and throws strikes, but his fastball is straight and his breaking ball has lagged. He is just 20, not yet out of A-ball, and if the slider he turned to late last season progresses, the righty could pitch toward the top of a rotation. But players with just this kind of profile also have ended up in bullpens because the full repertoire has failed to mature.

No doubt, the Alderson administration receives high marks for passing the theory portion of this exam, performing a rationale act well. But the final grade is always about results, not concepts. Which means the Mets have to reverse recent history when it comes to the return on a pitcher such as Dickey, or else the Alderson years just might be remembered for inadequa-Cy.